The invention generally concerns a method for extracting materials from plants using pressurized aqueous compositions.
Herbal remedies are becoming increasingly popular for treating certain conditions. For example, in 1998 an estimated 10.8 million Americans used Ginkgo biloba extract, which supposedly increases memory and promotes blood thinning. Other examples of popular extracts and their purported effects include extracts of Echinacea for bolstering the immune system and extracts of St. John""s wort for mood elevation.
Plant materials often have complex compositions that can vary with source and time of year, and therefore it is difficult to provide extracts of consistent quality to consumers. Furthermore, plant extract quality variabilities are exacerbated by the methods used to produce the extract. Consistent quality is especially important for extracts ingested by humans for medicinal purposes.
Solvent boiling is a common method used to prepare plant extracts. Water, or mixtures of water and various organic solvents, such as ethanol or acetone, are added to the plant material and boiled to extract the desired compounds. Solvent boiling is not selective, and therefore the extract obtained typically contains many compounds besides the desired ingredients. Another disadvantage of solvent boiling methods is the potential decomposition during the heating process of thermally labile, biologically active compounds.
Although some plant constituents can be synthesized, the major sources of such complex natural products are still the plants themselves. Therefore, in order to recover desired plant components in maximum amounts, more efficient and selective extraction methods are needed. In addition, environmentally responsible methods, which eliminate the need for organic solvents and thereby reduce disposal costs and the danger posed by exposure to such solvents, are desirable.
The present invention addresses the objectives discussed in the Background. One embodiment of the present method for extracting materials from a plant comprises providing a plant sample, and then exposing the plant sample to a liquid aqueous composition. Exposing the plant sample to a liquid aqueous composition can be done statically, dynamically, or both. The sample is exposed to a liquid aqueous composition at a temperature of from about 0xc2x0 C. to about 100xc2x0 C. and a pressure between about 25 atm and about 1000 atm, more typically from about 50 atm to about 200 atm. Plant materials are selectively isolated in the aqueous compositions by this method more effectively than prior methods. Moreover, the present method provides facile extraction of thermally labile compounds, such as bilobalides from ginkgo leaves.
Mesh size can effect the extraction results. For terpene trilactones, such as ginkolides and bilobalides, the sample is pulverized and screened to a particle size of between about 20-mesh and about 80-mesh, preferably from about 42-mesh to about 60-mesh, before exposing the plant material to the liquid aqueous composition. Flow aids, such as sand, can be mixed with the sample to facilitate liquid flow through, around and about the plant material. Where the plant sample is from the genus Gingko, the method typically uses an aqueous compositions at a temperature between about 0xc2x0 C. and about 100xc2x0 C., more typically 0xc2x0 C. and about 80xc2x0 C., and preferably between about 0xc2x0 C. and about 60xc2x0 C.
Terpene trilactones selectively extracted from plant material by the present pressurized water extraction (PWE) method may have the following Formula I, which is representative of the ginkolides. 
With reference to Formula I, R1 is selected from the group consisting of xe2x80x94H and xe2x80x94OH; R2 is selected from the group consisting of xe2x80x94H and xe2x80x94OH; R3 is selected from the group consisting of xe2x80x94H and xe2x80x94OH; R4 is selected from the group consisting of xe2x80x94H and lower aliphatic, particularly lower alkyl, such as methyl; and R5 is selected from the group consisting of xe2x80x94H, xe2x80x94OH, and lower aliphatic, particularly sterically hindered lower alkyl groups, such as isopropyl, t-butyl or neopentyl.
The terpene trilactone also may have the following Formula II, which is representative of the bilobalides. 
With reference to Formula II, R1 is selected from the group consisting of H and xe2x80x94OH; and R2 and R3 are independently selected from the group consisting of xe2x80x94H, xe2x80x94OH, and lower aliphatic, particularly lower alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl and t-butyl.
The PWE method allows extractions to be conducted at relatively low temperatures, e.g., below about 100xc2x0 C., compared to known methods. Thus, a currently preferred method involves a room temperature method for extracting terpene trilactones from plants; particularly terpene trilactones soluble or at least partially soluble in water or aqueous based solutions. Such extractions can be quantitative. This embodiment of the present PWE method comprises providing powdered plant material having a mesh size between about 42-mesh and about 60-mesh, passing aqueous compositions through the powdered plant material at a temperature less than 100xc2x0 C. and a pressure of at least about 50 atm (e.g., about 100 atm), and isolating material solubilized in such aqueous compositions.
The term aqueous composition as used herein includes, but is not limited to, pure water (e.g. distilled, doubly distilled, or deionized water), substantially pure water, and aqueous solutions containing modifiers. Substantially pure water refers to water containing dissolved or suspended materials that are not intentionally added to facilitate extraction of materials. Tap water, ground water, partially deionized water, and surface water are non-limiting examples of substantially pure water.